This invention relates to a brake pressure control valve adapted for use in a dual-system type hydraulic braking system of a vehicle.
It is known to arrange a brake pressure control valve in a hydraulic braking system of a vehicle for controlling the brake pressure delivered to the rear wheels of the vehicle so as to change the ratio between the brake pressure delivered to the rear wheels compared to the brake pressure delivered to the front wheels. The valve can permit maximum utilization of both front and rear brakes before skidding occurs. However, various brake pressure control valves heretofore proposed are intended to control the brake pressure in a single-system type hydraulic braking system. Thus, such valves cannot control the brake pressure in two or more braking systems and, in such case, an independent valve must be arranged in each of the independent braking systems.
In a dual-system type or a split-system type hydraulic braking system in which the brake cylinder of the right side rear wheel is connected to a pressure space in a master cylinder different from a pressure space in the master cylinder connected to the brake cylinder of the left side rear wheel, it is very difficult to maintain the operating characteristics of each of the pressure control valves disposed between each of the pressure spaces and each of the brake cylinders of the rear wheels perfectly identical moreover, the pressures supplied from the pressure spaces of the master cylinder are not necessarily equal, therefore, the braking force in each of the rear wheels will become unbalanced.